topic 3

• Which are the most acidic and alkaline pHs?

  0 = acid 14 = alkaline
• What happens to the concentration of hydrogen ions when you go up a pH?

  the concentration reduces by x10 (it gets 10x smaller)
• Which ions are always present in a solution of an alkali?

  OH-
• Which ions are always present in a solution of an acid?

  H+
• What is the general equation for when a base reacts with an acid?

  base + acid -> salt + water
• What is the name for the reaction in which a base reacts with an acid?

  neutralisation
• What is the ionic equation for neutralisation?

  (H+) + (OH-) -> H2O

  You don't need the brackets, i just added them to separate the signs :)
• What properties of a strong acid?

  - fully dissociate in water to release H+ ions

  - more corrosive

  - higher concentration of H+ ions

  - they ionise almost completely in water
• What are properties of a weak acid?

  - partially dissociate in water

  - their ionisation is a reversible reaction

  - less corrosive

  - lower concentration of H+ ions
• What is the general equation for when an acid reacts with a metal?

  Acid + Metal -> Salt + Hydrogen
• What is the general equation for when an acid reacts with a metal carbonate?

  Acid + Metal Carbonate -> salt + water + carbon dioxide
• What is the general equation for when an acid reacts with a metal hydroxide/ a metal oxide?

  Acid + Metal hydroxide/ metal oxide -> salt +water
• What is the solubilty of chorides?

  Common chlorides = soluble, silver/ lead chloride = insoluble
• What is the solubility of nitrates?

  soluble
• What is the solublity of sulphates?

  Soluble, except lead, barium and calcium sulfate
• What is the solubility of carbonates and hydroxides?

  Insoluble, except for sodium, potassium and barium ones
• How can you make an insoluble salt?

  Add the appropriate base and acid each to separate beakers of deionised water (to ensure there are no other ions present), and shake each one to dissolve them. Then mix them. The insoluble salt should then form a precipitate, which you can filter out. You should rinse it with deionised water to remove excess solution, and then scrape onto fresh filter paper and leave to dry in a dessicator.
• How can you make a soluble salt?

  Heat acid in a water bath (to speed up reaction) inside a fume cupboard, to avoid releasing acid fumes into the room. Then add the base in excess to ensure all the acid will react. They will react to form a soluble salt. You should filter the solution to remove excess base, then heat gently in an evaporating dish until some of the water has evaporated so the mixture is more concentrated. Then leave to cool before placing in a warm place and leaving for the rest of the water to evaporate so that the solid salt can crystalise.
• How can you make an insoluble salt using titration?

  - measure a set amount acid into a flask using a pipette

  - add a few drops of single indicator and place the flask on a white tile to clearly see the colour change

  - slowly add in the alkali using a burette until you reach the end point

  - record the amount of alkali needed, and repeat the reaction but with no indicator. Then evaporate the water, and leave in a warm place to form crystals.
• What is electrolysis?


  the breakdown of a substance containing ions by electricity (using a d.c. supply)
• What are the two electrode called in electrolysis?

  the cathode and the anode.
• What is the charge of cations, and where are they attracted to during electrolysis?

  they are positive, and they are attracted to the cathode
• What is the charge of anions, and where are they attracted to during electrolysis?

  they are negative, and they are attracted to the anode
• What are the rules at the cathode for the electrolysis of an aqueous solution?

  - if hydrogen and metal ions are present, hydrogen gas will always be produced at the cathode, unless a metal less reactive than hydrogen, like copper or silver, is present, in which case a pure layer of that metal will be formed instead.
• What are the rules at the anode for the electrolysis of an aqueous solution?

  If OH- and halide ions (Cl-, Br- or I-) are present, the molecules of chlorine, bromine or iodine will be formed. If no halide ions are present, then oxygen will always be formed.
• If molten Lead Bromide was electrolysed, what would happen at the cathode?

  The positive lead cations would be attracted to the negative cathode, where they would gain electrons to form molten lead
• If molten Lead Bromide was electrolysed, what would happen at the anode?

  The negative bromide ions would be attracted to the positive anode, where they would lose electrons to form bromine gas.
• If a solution of copper sulphate was electrolysed (with inert electrodes) what would be produced at the anode and cathode?

  - an the anode oxygen gas would be produced, because to halide ions are present

  - at the cathode, copper would be produced because it is less reactive than hydrogen
• What would happen at the cathode if copper sulphate was electrolysed using reactive copper electrodes?

  The copper ions would be reduced at the pure copper cathode, meaning they would gain electrons to form pure solid copper.
• What would happen at the anode if copper sulphate was electrolysed using reactive copper electrodes?

  The copper atoms in the anode would be oxidised, meaning they would lose electrons to become copper ions, and would dissolve into the solution.
• How can electrolysis be used to obtain pure copper from impure copper?

  If the cathode was pure copper, and the anode was impure copper.

  - at the anode, the copper atoms would be oxidised to form ions which would dissolve into the solution and be attracted to the cathode.

  - the impurities in the anode would sink to form a sludge at the bottom of the beaker.

  -meanwhile, the copper cations would be attracted to the pure copper cathode, where they would gain electrons (be reduced) to form atoms - pure copper.